Element with a laminated metal structure

ABSTRACT

The problem of manufacturing heat-resistance elements with a laminated structure, comprising a plate of a metal having a comparatively low melting point, aluminum for example, is solved through coating this plate with a film of another metal having both a higher melting point and a high mechanical resistance allowing the holding in position of the aluminum plate when the latter is in the molten state. The aluminum plate can thus be brazed to another plate by means of a high temperature, and therefore reliable brazing, using a soldering metal or alloy whose melting point is higher than that of the aluminum.

United States Patent Doucerain [451 Mar. 21, 1972 [54] ELEMENT WITH ALAMINATED 2,916,337 12/1959 Fike ..29/l96.2 x METAL STRUCTURE 3,064,11211/1962 Hanzel ..29/197 X 3,090,118 5/1963 Hanzel 29/197 X [72]Inventor: Jacques J. D. Doucerain, Massy, France 3393446 H1968 Hughes etaL 29/197 X [73] Assignee: Societe de Traitements Electrolytiques et3,436,805 4/1969 Friske et 29/196-2 x E| g gh mi S 3,473,216 10/1969Webb ..29/198 X [22] Filed: Sept 1969 Primary Examiner--L. DewayneRutledge 211 App], 3 0,727 Assistant Examiner-E. L. WeiseAttorney-Cushman, Darby & Cushman [30] Foreign Application Priority Data[57] ABSTRACT Sept. 251 1968 :rance ..167S77 The problem ofmanufacturing heat resistance elements with Nov. 5, 968 rance ..172607 alaminated structure comprising a plate ofa metal having a comparativelylow melting point, aluminum for example, is E; Cl solved through coatingthis plate with a film of another metal 58 M is h 29/196 2 198 194having both a higher melting point and a high mechanical re- 1 0sistance allowing the holding in position of the aluminum plate when thelatter is in the molten state. The aluminum plate can [56] ReferencesCited thus be brazed to another plate by means of a high tempera UNITEDSTATES PATENTS ture, and therefore reliable brazing, using a solderingmetal or alloy whose melting point is higher than that of the aluminum.2,687,565 8/1954 Schaefer et al. 2,798,843 7/1957 Slomin et al. ..29/l98X 11 Claims, 3 Drawing Figures Patented March 21, 1972 2 Shasta-Shut 11N DUC TOR Patented March 21, 1972 2 Shoots-Shut l REGULATOR eENERMbRINDUCTOR ELEMENT WITH A LAMINATED METAL STRUCTURE The present inventionrelates to elements with a laminated metal structure which, in use, comeinto contact with heat sources and in particular to heater elementswhich constitute the bases of cooking vessels.

It is well known to produce easily maintained heater elements which havehigh mechanical strength and provide substantially uniform distributionof the heat over their surface, by making them of a plate having goodthermal conductivity, covered on at least one face by a plate ofstainless steel, the latter for example being part of a larger plateworked, for example by press-forming, in order to constitute a cookingvessel.

The metal having the good thermal conductivity is frequently copper.Other metals or metal alloys, in particular aluminum, however, are moresuitable because of their lower price and their better thermalconductivity for the same weight of metal used.

However the methods currently known for soldering an aluminum plate to aplate of stainless steel, present difficult problems:

Processes which employ melting are costly and require very delicatehandling to achieve perfect bonding, and processes which employ brazinghave to use soldering agents (metals or alloys) having a relatively lowmelting point, and at any rate lower than that of aluminum, in order toprevent melting. Brazing solders of this kind are liable to corrosionand can be destroyed by heat because of their low melting point.

The object of the present invention is to overcome these drawbacks.

According to the invention, there is provided an element with alaminated metal structure comprising a first and a second plate, thebodies of said first and second plates being respectively made of afirst metal and of a second metal having a higher melting point thansaid first metal, said two pltes being brazed together through a layerof a soldering metal, the melting point of which is substantially lowerthan that of said second metal but too high for a brazing operationdirectly involving said first metal; the body of said first plate beingcoated, at least over that portion thereof which is in front of saidlayer, with a film of a third metal, said third metal having a highmechanical strength and a melting point substantially higher than thatofsaid soldering metal.

The present invention has also for its object a method for manufacturinga two-plate element according to the invention.

The invention will be best understood and other characteristics thereofwill appear by means of the following description and appended drawingsin which:

FIG. 1 is a section through a cooking vessel comprising a laminatedmetal element in accordance with the invention;

FIG. 2 is a section through an arrangement for carrying out the methodaccording to the invention.

FIG. 3 is a section through a further laminated element according to theinvention.

For conveniences sake, throughout the description and claims the wordmetal" should be understood as meaning either a homogeneous metal, or ametal alloy, whether the plates of the strafified element, the coating,or the soldering agent are concerned.

In FIG. 1, the base 2 of the vessel 1 of stainless steel, is covered bya plate 3 having an aluminum body entirely clad in a film of highstrength metal 4 and bonded to the base 2 by brazing using the solderingmetal 5. The plate 3 in turn is covered by a plate of stainless steel 7,by brazing using a soldering metal 6 identical to the soldering metal 5.The arrow 8 indicates the direction in which pressure has to be appliedin order to obtain proper brazing, the latter being effected using theinductor 9 which may be of any conventional kind and is supplied from ahigh frequency generator (not shown).

The heater element in accordance with the invention is essentiallyformed by the stainless steel plate 2, integral with, and forming thebase of, a vessel 1, and by the aluminum plate 3 whose encapsulatingfilm 4 must satisfy the following specific requirements:

a melting temperature higher than that of the coated metal;

high mechanical strength;

adhesion to, and total compatibility with, the coated metal;

corrosion-resistance;

zero toxicity (at least as concern cooking vessels);

capability of being brazed to stainless steel.

Phosphor-nickel is an example of a metal which will satisfy theserequirements if the coated metal is aluminum and is to be brazed tostainless steel, as in the case of the present example in which acoating of some 30 microns thickness can be used with a conventionalsoldering alloy whose melting point is around 680 C.

A pressure of 3 to 5 kg. per cm. has to be exerted during the heatingdue to inductor 9.

During brazing, the phosphor-nickel film exercises the following twofunctions:

it substitutes itself for the aluminum, in the brazing process;

it ensures the holding in position of the aluminum which melts duringthe brazing operation; the aluminum is held in a sort of skin of highstrength metal and does not suffer any appreciable distortion.

In fact, such a film is necessary even where the melting point of thesoldering agent, for example an alloy melting at 620 C., is onlyslightly lower than that of the aluminum, since the plates are to bebrought to a temperature higher than the melting point of the solderingagent if a reliable brazing is to be obtained.

After brazing, it is of course possible to dispense with that part ofthe coating which is situated beyond the joint. However that face of thecoating which is opposite to the plate 2, may also be used, as in theexample shown, to cover the plate 3 externally with a stainless steelplate 7 brazed on simultaneously under the same conditions as the plate2.

The previously described arrangements have been found to be particularlyadvantageous since the heat required to produce the melting temperaturein the brazed joint is produced by a heat source, the arrangement ofwhich is such that the heat is transmitted to the base 2 through thewhole of the thickness of the aluminum plate which melts in itsentirety.

In the case where the heater element does not comprise a secondstainless steel plate on the other face of the aluminum plate, such aprocess may appear to be something of a paradox; however, it isjustified on the one hand by practical and industrial considerations, inparticular by the excellent temperature distribution which it secures inthe brazed joint, and on the other hand by the simplification of themanufacturing arrangement.

However, the melting of the totality of the aluminum plate makes itnecessary to give the metal coating which keeps the molten aluminum inposition, a substantial thickness.

It is possible to overcome this drawback by another manufacturingmethod.

In FIG. 2, where references identical to those used in FIG. 1 relate tothe same parts, the base 2 of the vessel 1 of stainless steel, iscovered by an aluminum plate 3'which is clad in a coating ofphosphor-nickel 4, the base and the plate being separated by a layer ofsoldering metal 5.

The face of the base 2 which is opposite to the aluminum plate 3, iscovered by a plate of refractory dielectric material 11, itself coveredin turn by an inductor 9 supplied from a high frequency generator 12 andits regulator 19. That face of the plate 3 which is opposite to the base2 is covered by a metal slab 14 with internal ducts 18 having externalentrance 16 and exit 17 allowing the circulation of water in ducts 18.The stacked arrangement thus produced is inserted between two pressplates 13 and 15 which exercise a force in the direction of thecorresponding arrows 20 and 21.

Brazing proper is carried out under the same conditions as thosepreviously described, but the heat source, thanks to the arrangementused, operates with maximum efficiency in that part of the plate 3located close to the brazing solder, the plate of refractory material 11helping to ensure uniform distribution of heat. On the other hand, thatpart of the plate 3 located opposite to the soldering metal, issubmitted to the action of the cold body 14 and this produces, throughthe thickness of the plate 3, a substantial temperature gradient whichis such as to maintain solid that part which is in contact with the coldbody 14 whilst the part in contact with the hot source is in the moltencondition.

As a consequence, the thickness of the coating may be reduced; it isalso possible to coat the plate 3 only on those portions thereof whichare liable to melt; in any case that portion of the surface of plate 3which is in contact with the soldering agent must obviously be coated.

This condition of thermal equilibrium which may at first sight appear tobe a precarious one, can in fact be very easily maintained during thetime required for brazing, provided that the supply of energy by the hotsource and the extraction of energy by the cold body 14, are properlyregulated.

The supply by energy to the hot source is obtained by regulating thehigh frequency current in the inductor 9 by any suitable known means 19.

Regulation of the extraction of energy through the cold body is obtainedby regulating the flow of water through the component 14, this waterbeing injected at a fixed temperature.

The above structures and methods of course also apply where the platewith the higher melting point is of a substance other than stainlesssteel.

However, in some cases, some difficulties may arise, in particular asconcerns adhesion, which difficulties can be solved through coating alsothe plate with the higher melting point with a film of the same natureas that which is used for the plate with the lower melting point. InFIG. 3, the aluminum cylindrical component 10, a base of which, 103,forms one of the plates of a laminated element, is entirely coated witha film 104 of phosphor-nickel. A circular titanium plate 102, alsocoated with a film 40 of phosphor-nickel, adheres to this flat circularbase 103 through the soldering agent 105.

The brazing may be effected according to the above described methods,elements 102, 103, 104 and 105 of FIG. 3 respectively playing the partof elements 2, 3, 4 and of FIGS. 1 and 2.

Since the purpose ofthe film 40, coating the plate 102, is essentiallyto facilitate the adhesion to the soldering agent, this film need notnecessarily coat the whole of the surface of the plate 102. Inparticular, if this latter plate forms part ofa complex mechanicalcomponent, the coating may be limited to the surface in contact with thesoldering agent.

The invention can in particular advantageously be applied in themanufacturing of pistons for internal combustion engines, where thosepistons are made of an aluminum alloy, and it is desired to protecttheir tops by means of a titan plate improving their resistance to theaction of burning or corrosive gases.

What is claimed, is,

1. An element with a laminated metal structure comprising a first and asecond plate, the bodies of said first and second plates beingrespectively made of a first metal and of a second metal having a highermelting point than said first metal, said two plates being brazedtogether through a layer of a soldering metal, the melting point ofwhich is substantially lower than that of said second metal but too highfor a brazing operation directly involving said first metal; the body ofsaid first plate being coated, at least over that portion thereof whichis in front of said layer, with a film of a third metal, said thirdmetal having a high mechanical strength and a melting pointsubstantially higher than that of said soldering metal.

2. An element as claimed in claim 1, wherein the melting point of saidfirst metal is lower than that of said soldering metal. 7

3. An element as claimed in claim 1, wherein the melting point of saidfirst metal is substantially equal to that of said solderin metal.

4. in element as claimed in claim 1, wherein said film coats the wholeof the surface of said body of said first plate.

5. An element as claimed in claim 1, comprising only said two plates,said first metal being aluminum and said second metal being stainlesssteel.

6. An element as claimed in claim 1, wherein said first metal isaluminum and said second metal stainless steel, and said elementcomprises a further plate of said second metal; said first plate beinginserted between said second plate and said further plate and beingbrazed to said further plate through a further layer of said solderingmetal, and the body of said first plate being coated with a further filmofsaid third metal.

7. An element as claimed in claim 1, wherein said third metal isphosphor-nickel.

8. An element as claimed in claim 1, wherein said film is a film whichhas been deposited by a chemical process.

9. An element as claimed in claim 1, wherein, said element comprisingonly two plates, the body of said second plate is also coated, at leastover that portion of the surface thereof, which is in front of saidlayer, with a film of said third metal.

10. An element as claimed in claim 9, wherein said second metal istitanium.

11. An element as claimed in claim 1, wherein at least one of said twoplates is an integral part of a component made of the same metal as thisplate.

2. An element as claimed in claim 1, wherein the melting point of saidfirst metal is lower than that of said soldering metal.
 3. An element asclaimed in claim 1, wherein the melting point of said first metal issubstantially equal to that of said soldering metal.
 4. An element asclaimed in claim 1, wherein said film coats the whole of the surface ofsaid body of said first plate.
 5. An element as claimed in claim 1,comprising only said two plates, said first metal being aluminum andsaid second metal being stainless steel.
 6. An element as claimed inclaim 1, wherein said first metal is aluminum and said second metalstainless steel, and said element comprises a further plate of saidsecond metal; said first plate being inserted between said second plateand said further plate and being brazed to said further plate through afurther layer of said soldering metal, and the body of said first platebeing coated with a further film of said third metal.
 7. An element asclaimed in claim 1, wherein said third metal is phosphor-nickel.
 8. Anelement as claimed in claim 1, wherein said film is a film which hasbeen deposited by a chemical process.
 9. An element as claimed in claim1, wherein, said element comprising only two plates, the body of saidsecond plate is also coated, at least over that portion of the surfacethereof, which is in front of said layer, with a film of said thirdmetal.
 10. An element as claimed in claim 9, wherein said second metalis titanium.
 11. An element as claimed in claim 1, wherein at least oneof said two plates is an integral part of a component made of the samemetal as this plate.